The heat-pump model changed after the electrical quote: what must be rechecked?

Identify the equipment revision before purchase

The recorded homeowner discussion asks who handles a central heat pump's electrical hookup. It supports a trade-coordination concern, not a claim about a documented nameplate substitution. The model-change scenario here is illustrative: an electrical quote prepared for one indoor unit, outdoor unit and heater combination may no longer fit a substituted package.

Source: Central Heat Pump - Who does electrical hookup

Read MCA and MOCP for the complete combination

MCA means minimum circuit ampacity: the equipment value used to establish the required supply-conductor ampacity, with applicable installation adjustments. MOCP, also labeled MOP, means maximum overcurrent protection: the permitted upper limit for the specified protective device. Neither is simply the unit's normal operating current. Read the selected equipment's instructions and nameplate instead of deriving a breaker from cooling tonnage.

Mitsubishi's electric-heat manual illustrates why the heater needs its own equipment schedule. Table 3-2 lists EH10-SVZ-M at 10 kW and 41.7A heater current at 240V, with MCA 52.1A and MOP 60A for the heater-only supply. When that circuit also supplies the air-handler motor, the table gives MCA 56.2A and MOP 60A. At 208V the kit produces 7.5 kW; the corresponding electrical values also change. The heater kit requires its own power supply and must not receive power from the outdoor unit. The manual requires the building circuit breaker to be sized per the MOP listed for the supplied voltage. The kit's factory-installed breaker serves only as a disconnect switch. The 41.7A operating-current figure is neither the conductor-sizing basis nor a breaker recommendation. These values describe this listed combination, not heat pumps generally.

Source: Mitsubishi Electric US: electric heat installation manual, July 2023 · Mitsubishi heat pump submittal: separate MCA and MOCP fields (2018 example)

Illustrative scenario: resistance heat is added late

Illustrative scenario: an owner approves a heat-pump proposal without resistance backup heat, and the electrician prices the associated supply. A later HVAC revision adds an auxiliary heater to address a design concern. The new load may require a different circuit, feeder assessment, or service calculation. If the change reaches the electrician only after equipment delivery, the project can face rework or a delay that neither trade included in its original schedule.

The added heater may be a much larger electrical change than the compressor substitution. The HVAC designer should justify auxiliary heat and specify its supported controls; the electrical provider then assesses the resulting configuration. A verbal promise that backup heat will rarely operate is not a circuit-design basis.

Create one indoor, outdoor and heater schedule

Create a shared equipment schedule before final electrical pricing. Include indoor and outdoor model numbers, supplied accessories, auxiliary heat, disconnect requirements, and the division of work between trades. Ask the HVAC designer to identify the basis for heating capacity and backup heat rather than assuming the largest available package is necessary. The electrician should verify the resulting electrical scope, including any removed loads that the new system replaces.

Check substitutions before release

Require a substitution check before purchase. The revised model should be compared against the electrical schedule and any incentive qualification, not only against the quoted efficiency or tonnage. Assign responsibility for obtaining updated specifications and for revising permits where required. If a circuit was preinstalled for future equipment, record its actual rating and route; do not promise compatibility with every later heat pump.

Match the installed equipment and control settings

At commissioning, confirm that installed equipment matches the approved schedule and that auxiliary modes are configured as intended. The homeowner should understand which settings are normal user controls and which require the HVAC or electrical provider. Keep the final model information and circuit records together for future service. Clear coordination prevents the electrical installation from becoming a surprise discovered after the heating system is already on site.

Use a change checklist before the substitute is released

Release the substitute only after the HVAC provider confirms the supported combination and performance, the electrician confirms the supply, and the permit coordinator resolves affected documents. Refer all approvals to the same model schedule. Record any supported auxiliary-heat control constraint for future service technicians; a later request to enable another mode must be checked against that electrical basis.

Put it into practice

A decision table to keep handy